1. Field of the Invention
The present invention relates to wireless communication networks, specifically to reducing interference in a wireless communication network through channel selection.
2. Description of the Related Art
In communications systems, there is an ever-increasing demand for higher data throughput. There is a corresponding drive to reduce interference that can disrupt such communications systems.
The Institute of Electrical & Electronic Engineers (IEEE) 802.11b and 802.11g wireless local area network (WLAN) specifications divide the 2.4 gigahertz (GHz) spectrum into 14 overlapping, staggered channels. The center frequency for each of these channels is five megahertz (MHz) apart. The 802.11b and 802.11g standards further specify a spectral mask width to power level for each channel. For example, the spectral mask for 802.11b requires that the signal be attenuated by at least 30 dB from its peak energy at +11 MHz from the center frequency. As a result, an 802.11b compliant transceiver occupies five channels to an energy level of 30 dB down from the peak or center of the signal. In the United States—per Federal Communications Commission (FCC) mandate—the valid channels are one through eleven meaning that the number of non-overlapped channels is limited to channels 1, 6, and 11.
In an 802.11 compliant wireless communication network, an access point such as a base station acts as a bridge between a WLAN and a wired local area network (LAN). The access point communicates data with one or more remote receiving nodes over a wireless link in the WLAN. Due to the limited number of non-overlapped channels, the wireless link may be susceptible to interference from other access points and radio transmitting devices. The interference may force communication at a lower data rate or completely disrupt the wireless link all together.
Further, the radio spectrum is subject to arbitrary interference, which may vary from channel-to-channel. For example, the 802.11b and 802.11g standards both utilize the aforementioned 2.4 GHz band. As a result, interference may be generated from the likes of microwave ovens, cordless telephones, and Bluetooth devices. Certain components in a radio communication system (e.g., a digital subsystem) may also produce local noise. This arbitrary interference may pose a problem in that many radio communication system components have frequency-dependent performance characteristics.
To address the issue of interference in a WLAN, many access points include automatic channel selection capabilities. Automatic channel selection involves an access point attempting to identify a channel free or substantially free from interference from amongst available wireless channels. The access points then ‘jumps’ from channel-to-channel to avoid interfering conditions. In a wireless environment with a number of access points (e.g., a mesh network), an access point senses the presence of other access points and attempts to adjust to a quieter channel when interference from the other access points is detected.
Most automatic channel selection algorithms operate on an open-loop model. In an open-loop model, interference is evaluated only at the victimized access point while interactions between the interfering access point and the victimized receiver are ignored. Open-loop evaluation generally consists of a ‘receive only’ mathematical analysis technique based on a probability of packet collision in time and frequency. Open-loop selection algorithms do not consider differential environmental conditions that exist between an access point and each receiver and further fail to consider different transmit power levels. Open-loop channel selection algorithms also fail to consider frequency-specific noise local to the clients.
Implementation-specific problems also exist with respect to sampling frequency in current open-loop automatic channel selection algorithms. For example, automatic channel selection may occur only at startup. A particular instance of interference may not exist during startup of a particular communication system and, instead, arise during a communication session. In this instance, an open-loop automatic-channel selection algorithm would fail to invoke an appropriate channel adjustment.
Interference, noise, and component frequency response are asymmetric and differentially affect radio transmitters and receivers. As such, optimizing radio system performance requires selecting an optimal channel that takes all of these effects into account. There is a need in the art for an automatic-channel selection solution that takes into account these effects at any time during a communication session.